In gas turbine engines a casing assembly is provided to house and support a number of rotors such as fan, compressor and turbine rotors. A conventional casing assembly may include a fan case, an intermediate case, a compressor case, a gas generator case, a turbine case and turbine exhaust case arranged about a central axis of the engine. The individual cases may be connected one to another for example by flanges and fasteners. A spigot joint may be provided between two connected cases such as the intermediate and compressor cases in order to provide concentricity control of the two cases. However, different cases may be made of different materials which have different thermal expansion coefficients. This may cause excessive tightening of the spigotted joint which can in turn cause high stress areas near the spigotted joint during engine operation. These high stress areas may be at locally stiff features such as bosses, discrete struts or supports, etc. and therefore may be at risk of component damage such as strut cracking.
Therefore, improved case joints are needed to relieve local loads generated by a tight spigot while maintaining concentricity control of the mating parts.